9027: feat: Attribute completion is context aware r=Veykril a=Veykril
This splits off the `lint` and `derive` completions into their own submodules of `attribute`.
The idea is to create a lazy global hashmap that maps `SyntaxKind` to attribute names(`&[&str]`) in which we index with the syntax kind of the "thing" we are attributing giving us the attributes back that are valid for this kind. Then we use this name to do a binary search on the attribute list to fetch and build the corresponding completion item.
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
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